A technique of IKE (Internet Key Exchange) has been known as a technique of performing a two-way authentication and sharing an encryption key between two devices (information processing apparatuses). There are basically two methods in this technique; a method based upon a public key cryptosystem, and a method based upon a pre-shared key.
The method based upon the public key cryptosystem is excellent in reducing cost for a key management, but computation cost increases. The method based upon the pre-shared key is excellent in reducing computation cost, but cost for the key management increases. For example, under a situation in which a device is subject to attack, and hence, secret information is leaked, the method based upon the public key cryptosystem can easily reconstruct the system. On the other hand, the method based upon the pre-shared key needs much cost for the reconstruction of the system.